JP2000133436A - Graphite electrode for electric furnace - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a graphite electrode for an electric furnace having sufficient contact area of a graphite electrode body and graphite nipple, dispersed thermal and mechanical stress and increased absolute strength of a screw thread. SOLUTION: In a graphite electrode 1 for an electric furnace formed by successively connecting plural graphite electrode bodies 2 provided with a female screw part 3 and a graphite nipple 4 threadedly engaged with the female screw part 3, if the screw pitch (p) of the female screw part 3 and the graphite nipple 4 is made more than 8.467 mm and not more than 25.4 mm (8.467 mm<p<=25.4 mm), a contact area in the connection part of the graphite electrode body 2 and the graphite nipple 4 can be sufficiently secured, a stress concentration factor of the screw root decreases, thermal and mechanical stress is avoided to be concentrated on some part of the screw roots of both, and since the screw thread itself is big, absolute strength of the screw increases, so that damage of the screw thread is reduced and it is effective to reduce occurrence of breaking troubles of the connection part. In addition, even if the radius of curvature (R) of the screw root of the female screw 3 and the graphite nipple 4 is made more than 0.76 mm and not more than 4.57 mm (0.76<R<=4.57 mm), same effect can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a graphite electrode for an electric furnace in which a female screw portion is provided on a graphite electrode main body, a graphite nipple is screwed into the female screw portion, and the graphite electrode main body is sequentially connected.

[0002]

2. Description of the Related Art A conventional graphite electrode for an electric furnace is designed and designed according to JIS standards for its joint structure. Graphite electrodes for electric furnaces of this design specification are not suitable for recent high-load operation of electric furnaces, and frequently cause breakage accidents.
Therefore, various proposals have been made to modify this JIS standard to prevent breakage accidents. For example,
The graphite electrode for an electric furnace according to Japanese Patent No. 39893 discloses a female screw part and a graphite nipple of a graphite electrode main body, in which a screw surface that is in contact with each other is set at an inclination angle of 15 degrees or less with respect to a plane perpendicular to the axis of the graphite electrode main body. Absorbs or suppresses thermal expansion in the direction perpendicular to the axis of the graphite electrode body, that is, in the radial direction, eliminates or reduces the occurrence of this thermal stress in the radial direction, and causes cracks in connection parts, breakage of screws, etc. This is to prevent accidents.

Further, the graphite electrode for an electric furnace disclosed in Japanese Utility Model Publication No. 56-16069 has the length of the graphite electrode body defined by JIS.
By making the length longer than the standard and making the length of the graphite nipple twice the maximum diameter of the graphite nipple, the breaking force at the bottom of the female screw portion of the graphite electrode main body, which causes breakage, is reduced. In other words, this pressing force is based on a half length of the graphite nipple,
This occurs in such a manner that the mouth of the female screw is used as a fulcrum and the end of the graphite nipple located at the bottom is used as a point of action.
It is longer than the IS standard, reduces the force applied to the point of action, and further increases the mechanical strength due to the relatively thick bottom, which reduces the breakage accident due to both effects.

Further, the graphite electrode for an electric furnace disclosed in Japanese Utility Model Publication No. 59-7749 reduces the body expansion by screwing and connecting the graphite electrode bodies to each other with a graphite nipple shorter than JIS standard. The pressing force on the internal thread of the graphite electrode body caused by the thermal expansion due to the graphite nipple at the time is reduced, and the stress applied to the thread of the internal thread is
The thread is evenly distributed on the threads in the space, and the effects of both reduce the possibility of breakage at the bottom of the female screw portion.

In a graphite electrode for an electric furnace disclosed in Japanese Utility Model Application Laid-Open No. 56-114098, the female screw portion of the graphite electrode body and the threaded portion of the graphite nipple are formed in an arc-shaped cross section, so that the graphite nipple is formed in the female screw portion. When screwing in the screw, a part of the screw thread does not drop off, the screwing is smooth, the contact is tight, and the concentration of stress does not occur, and the drop, breakage, loosening and falling accidents are reduced.

Further, the graphite electrode for an electric furnace disclosed in Japanese Utility Model Publication No. 58-958 continuously increases the thread height of the internal thread of the graphite electrode body and the graphite nipple from the small diameter side to the maximum diameter side. By cutting off a plurality of screw heads so as to gradually decrease, the moment applied to each of the above both threads forms a stress distribution that gradually decreases as it moves from the minimum diameter portion to the maximum diameter portion, It has a mitigating effect and reduces graphite nipple breakage accidents.

[0007]

The graphite electrode for an electric furnace described above has the effect of absorbing or suppressing the stress due to the thermal expansion in the radial direction, that is, the thermal stress, but it is directed to the mechanical stress. In this case, a breakage accident on this surface cannot be prevented, and the absolute strength of the screw thread is not improved, so that the screw cannot be damaged by mechanical external force. In addition, graphite electrodes for electric furnaces have the effect of reducing the pressing force due to mechanical stress on the bottom of the internal thread of the graphite electrode body due to the graphite nipple, but thermal stress is not particularly considered. However, it cannot cope with breakage of the screw due to mechanical external force. On the contrary, there are disadvantages such as material loss and processing increase due to the long graphite nipple. In addition, the graphite electrode for electric furnaces reduces the body swelling of the graphite nipple, thereby alleviating the pressing force on the female thread of the graphite electrode body, and increasing the stress applied to the thread of the female thread to increase the idle screw. Although it has the effect of reducing breakage at the bottom of the female screw part, the contact surface between the graphite electrode body and the graphite nipple cannot be avoided. It cannot respond to damage. In addition, graphite electrodes for electric furnaces can be screwed smoothly, and some of the threads do not drop off. It does not take care of mechanical stress and does not prevent breakage accidents on this surface, and it does not mean that the absolute strength of the screw has been improved, so it is possible to deal with breakage of the screw thread due to mechanical external force Can not. In addition, graphite electrodes for electric furnaces produce a stress distribution that gradually decreases as the moment applied to each thread transitions from the minimum diameter part to the maximum diameter part. While reducing accidents,
It is not treated against thermal stress, it can not prevent breakage accidents on this surface, and it does not mean that the absolute strength of the screw is improved, so it can not cope with damage due to mechanical external force of the screw thread .

Accordingly, it is an object of the present invention to disperse thermal and mechanical stress and to increase the absolute strength of both screws while ensuring a sufficient contact area between the graphite electrode body and the graphite nipple. It is an object of the present invention to provide a graphite electrode for an electric furnace which can prevent a breakage accident of the electric furnace.

[0009]

Means for Solving the Problems The present inventor has conducted intensive studies in order to achieve the above object, and as a result, has found that a sufficient contact area at the connection between the graphite electrode body and the graphite nipple, that is,
The screw concentration of the graphite electrode body and graphite nipple is made larger than the JIS standard while ensuring sufficient connectivity, so that the stress concentration coefficient of the thread valley becomes small, and thermal and mechanical It has been found that stress can be prevented from being concentrated, and the occurrence of breakage of the graphite electrode body and the connection portion of the graphite nipple can be reduced.In addition, if the screw pitch is large, the thread itself becomes large, and as a result, the screw The inventors have also found that the absolute strength is increased, the thread breakage is reduced, and the occurrence of breakage of the connection portion is reduced, and the present invention has been completed.

That is, the invention of claim 1 is a graphite electrode for an electric furnace, wherein a female screw portion is provided on a graphite electrode main body, a graphite nipple is screwed into the female screw portion, and a plurality of the graphite electrode main bodies are sequentially connected. And a thread pitch (p) of the female screw portion and the graphite nipple is more than 8.467 mm and not more than 25.4 mm (8.467 mm <p ≦ 25.4 mm). .

A second aspect of the present invention relates to a graphite electrode for an electric furnace, wherein a female screw portion is provided in a graphite electrode main body, and a graphite nipple is screwed into the female screw portion to sequentially connect the plurality of graphite electrode main bodies. Wherein the radius of curvature (R) of the female thread portion and the thread root of the graphite nipple is more than 0.76 mm and not more than 4.57 mm (0.76 mm <R ≦ 4.57 mm). Provided.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A graphite electrode for an electric furnace according to an embodiment of the present invention will be described below in detail with reference to FIGS. FIG. 1 is a side view in which a part of a graphite electrode for an electric furnace according to an embodiment of the present invention is cut away, FIG. 2 is a side view in which a part of a graphite electrode for an electric furnace according to an embodiment of the present invention is sectioned, FIG. 3 is a side view of a graphite nipple constituting the graphite electrode for an electric furnace of FIG. 2. In the drawing, reference numeral 1 denotes a graphite electrode for an electric furnace, and the graphite electrode 1 for an electric furnace has a female screw portion 3 on a graphite electrode body 2.
And a graphite nipple 4 is screwed into the female screw portion 3 to sequentially connect a plurality of graphite electrode bodies 2. The screw pitch p of the female screw portion 3 and the graphite nipple 4 is 8.467 mm.
Over 25.4 mm, that is, 8.467 mm <p ≦
It is in the range of 25.4 mm.

The graphite electrode body 2 generally has a female thread 3 at both ends in the axial direction, and a female thread 3 at one end and is used at the tip. Each of these graphite electrode main bodies 2 is screwed and connected by a graphite nipple 4 to form the graphite electrode 1 for an electric furnace. The graphite nipple 4 has a minimum diameter at both ends in the axial direction, and tapered threads at both ends where the middle has the maximum diameter. As shown in FIG. 4, this taper has a central axis length l of 3 and a radial length r of 1, but is not limited thereto. The female screw portion 3 of the graphite electrode body 2 screwed to the graphite nipple 4 is also a tapered screw. Since the thread 10 of the female thread portion 3 and the thread 11 of the graphite nipple 4 are both parallel to the pitch line, the thread is smoothly engaged and the tops of the threads 10 and 11 may be chipped. There is no. The bottom of the thread root 12 of the female screw portion 3 and the bottom of the thread root 13 of the graphite nipple 4 are curved.

The thread 10, 11 to the thread valley 12, 1
The screw pitch p of No. 3 is 8.467 mm <p ≦ 25.4 mm, and it is important that the screw pitch p be in this range. According to JIS R7201-1997 artificial graphite round electrode, two types of screw pitches are specified: 6.350 mm and 8.467 mm. Therefore, the thread pitch p of the present invention is larger than the JIS standard,
Although the thread valleys 12 and 13 become large and the number decreases, the contact area of these connection portions 14 hardly changes as a result of an increase in the area of one thread or thread valley. When the screw pitch p is within this range, the stress concentration factor becomes small, mechanical or thermal stress is dispersed, and breakage of the connecting portion 14 is reduced. If the screw pitch p is smaller than 8.467 mm, the thread pitch becomes the same as that of the conventional JIS standard, and the breakage of the connecting portion 14 occurs at the same frequency as the conventional one. Screw pitch p is 25.4
If it exceeds mm, in the example of FIG. 5, the threads 10, 11 to the thread valleys 12, 13 become too large to be practical.

Further, the graphite electrode 1a for an electric furnace of the present invention comprises:
The radius of curvature R of the thread root 20 of the female screw portion 3a of the graphite electrode main body 2a and the radius of curvature R of the thread root 21 of the graphite nipple 4a are both 0.7.
6 mm <R ≦ 4.57 mm. As described above, according to JIS R7201-1997 artificial graphite round electrode, the pitch of the screw is specified to be 6.350 mm and 8.467 mm. In the case of 6.350 mm, the radius of curvature of the screw root is 0.3 mm. In the case of 8.467 mm, the radius of curvature of the thread root is specified to be 0.76 mm or less. Therefore, it is important that the radius of curvature R of the thread root of the present invention is larger than 0.76 mm.
It becomes the same as that of the S standard, and the breakage accident of the connecting portion 14 occurs as in the conventional case. When the radius of curvature R of the thread valley exceeds 4.57 mm, the thread valley 20 and the thread valley 21 become too large in the example of FIG. In the graphite electrode 1a for an electric furnace of the present invention, the screw pitch p of the female screw portion 3a and the graphite nipple 4a is 8.
467 mm <p ≦ 25.4 mm, and the curvature radii R of the thread roots may both be 0.76 mm <R ≦ 4.57 mm.

Hereinafter, embodiments of the present invention will be described.
The effect is demonstrated based on it. It should be noted that these examples are for describing a preferred embodiment of the present invention, and the present invention is not limited thereto.

Example 1 First, a graphite electrode for an electric furnace for a test was prepared. This graphite electrode for an electric furnace is an electric furnace for 150 t steelmaking (transformer capacity).
(150,000kVA, electrode load 150kA, voltage 850V)
750mm (30in) x 2700mm long
(110 in), the internal thread of the graphite electrode body and the graphite nipple have a taper of 1/3, a thread angle of 60 degrees, a screw pitch of 12.700 mm, and a radius of curvature of a screw root of 1.14 mm.
And Using 110 graphite electrodes for electric furnace, 1
After continuous operation for a month, the number of breakage accidents of the graphite electrode for electric furnace is visually observed. Example 2 Screw pitch 10.583 mm, radius of curvature of screw root 0.95
The graphite electrode for an electric furnace was operated continuously for one month under the same conditions as in Example 1 except that the thickness was changed to mm, and the number of breakage accidents of the graphite electrode for an electric furnace was visually observed. Example 3 Screw pitch 22.166 mm, radius of curvature 4.14 of screw root
The graphite electrode for an electric furnace was operated continuously for one month under the same conditions as in Example 1 except that the thickness was changed to mm, and the number of breakage accidents of the graphite electrode for an electric furnace was visually observed.

Comparative Example 1 Screw pitch 6.350 mm, radius of curvature of screw root 0.57 mm
A graphite electrode for an electric furnace was operated continuously for one month under the same conditions as in Example 1 except that the number of breakage accidents of the graphite electrode for an electric furnace was visually observed. Comparative Example 2 Screw pitch 8.467 mm, radius of curvature of screw root 0.76 mm
A graphite electrode for an electric furnace was operated continuously for one month under the same conditions as in Example 1 except that the number of breakage accidents of the graphite electrode for an electric furnace was visually observed. Table 1 shows the measurement results of the number of breakage accidents of the graphite electrodes for electric furnaces of Examples 1 to 3 and Comparative Examples 1 and 2.

[0019]

[Table 1]

According to Table 1, one breakage accident occurred in Example 2, but compared to Comparative Examples 1 and 2, it was one-seventh.
It is 1/5 from the above, and it can be said that the effect of the present invention was confirmed.

[0021]

According to the first aspect of the present invention, by increasing the screw pitch between the graphite electrode body and the graphite nipple, the contact area at the connection between the graphite electrode body and the graphite nipple can be sufficiently ensured, and the screw valley can be formed. The stress concentration factor is reduced, and thermal and mechanical stress can be prevented from concentrating on some of the thread valleys.This has the effect of reducing the occurrence of breakage of the graphite electrode body and graphite nipple connection. is there. In addition, when the thread pitch is large, the thread itself becomes large, and as a result, the absolute strength of the thread is increased, so that damage to the thread is reduced, and there is an effect of reducing the occurrence of breakage of the connection portion due to this.

According to the second aspect of the present invention, the same effect as described above can be obtained by increasing the radius of curvature of the thread roots of the graphite electrode body and the graphite nipple.

[Brief description of the drawings]

FIG. 1 is a side view in which a part of a graphite electrode for an electric furnace according to an embodiment of the present invention is cut away.

FIG. 2 is a side view showing a cross section of a part of a graphite electrode for an electric furnace according to an embodiment of the present invention.

FIG. 3 shows a side view of a graphite nipple constituting the graphite electrode for an electric furnace of FIG. 2;

FIG. 4 is a conceptual diagram showing a taper of a graphite electrode for an electric furnace.

FIG. 5 is an enlarged sectional view showing a relationship between a graphite electrode main body and a graphite nipple.

FIG. 6 is an enlarged sectional view showing a relationship between a graphite electrode body and a graphite nipple of another embodiment.

[Explanation of symbols]

 1, 1a graphite electrode for electric furnace 2, 2a graphite electrode body 3, 3a female screw part 4, 4a graphite nipple 10, 11, screw thread 12, 13, 20, 21, screw thread 14 connection part

Claims (2)

[Claims] 1. A graphite electrode for an electric furnace, wherein a female screw portion is provided on a graphite electrode main body, a graphite nipple is screwed into the female screw portion, and a plurality of the graphite electrode main bodies are sequentially connected, wherein the female screw portion and the graphite nipple are provided. Has a thread pitch (p) of 8.46
Exceeding 7 mm and not more than 25.4 mm (8.467 mm <p ≦ 25.
4 mm) graphite electrode for an electric furnace. 2. A graphite electrode for an electric furnace, wherein a female screw portion is provided on a graphite electrode main body, a graphite nipple is screwed into the female screw portion, and a plurality of the graphite electrode main bodies are sequentially connected, wherein the female screw portion and the graphite nipple are provided. The radius of curvature (R) of the thread valley of 0.75 to 4.57 mm or more (0.76 mm <R ≦
4.55 mm). A graphite electrode for an electric furnace.